White Fluffy Mold

I bought an 'Annabelle' Hydrangea and put it in a sunny location in my backyard. Soon after, I noticed that it was not growing well, and some of the leaves were crispy and browning at the edges. On the soil around the plant, but not on the leaves, I put down a product labelled 'Bug geta' as I thought perhaps a fungus had attacked the plant. Shortly after, I noticed this fluffy white deposit in three distinct areas on the soil. Have I damaged the plant? What should I do to rectify the situation? I should mention that it has been very humid here in Hamilton, Ontario, Canada.